CS5253B-8GDP5 ONSEMI [ON Semiconductor], CS5253B-8GDP5 Datasheet - Page 7

• Manufacturer Part Number: CS5253B-8GDP5
• Description: 3.0 A LDO 5-Pin 2.5 V Fixed Linear Regulator for Remote Sense Applications
• Manufacturer: ONSEMI [ON Semiconductor]

Calculating Power Dissipation and Heatsink
Requirements
operate at high junction temperatures. Therefore, it is
important to calculate the power dissipation and junction
temperatures accurately to ensure that an adequate heatsink
is used. Since the package tab is connected to V
CS5253B−8, electrical isolation may be required for some
applications. Also, as with all high power packages, thermal
compound in necessary to ensure proper heat flow. For
added safety, this high current LDO includes an internal
thermal shutdown circuit
following four factors: junction temperature, ambient
temperature, die power dissipation, and the thermal
resistance from the die junction to ambient air. The
maximum junction temperature can be determined by:
dissipation are determined by the design while the
maximum junction temperature and the thermal resistance
depend on the manufacturer and the package type. The
maximum power dissipation for a regulator is:
High power regulators such as the CS5253B−8 usually
The thermal characteristics of an IC depend on the
The maximum ambient temperature and the power
PD (max) + ( V IN(max) * V OUT(min) ) I OUT(max)
+5.0 V
+3.3 V
T J(max) + T A(max) ) PD (max)
GND
) V IN(max)
+
10 mF
I IN(max)
+
100 mF
R qJA
V
V
CONTROL
POWER
Local
Connections
OUT
Figure 16. Remote Sense
CS5253B−8
http://onsemi.com
on the
CS5253B−8
7
V
SENSE
V
GND
OUT
package to improve the flow of heat away from the IC and
into the surrounding air. Each material in the heat flow path
between the IC and the outside environment has a thermal
resistance which is measured in degrees per watt. Like series
electrical resistances, these thermal resistances are summed
to determine the total thermal resistance between the die
junction and the surrounding air, R
resistance is comprised of three components. These resistive
terms are measured from junction−to−case (R
case−to−heatsink (R
(R
D
CS5253B−8 the majority of heat is generated in the power
transistor section. The value for R
heatsink type, while the R
package type, heatsink interface (is an insulator and thermal
grease used?), and the contact area between the heatsink and
the package. Once these calculations are complete, the
maximum permissible value of R
the proper heatsink selected. For further discussion on
heatsink selection, see our application note “Thermal
Management,” document number AND8036/D.
2
A heatsink effectively increases the surface area of the
The value for R
qSA
PAK−5 package. For a high current regulator such as the
). The equation is:
R qJA + R qJC ) R qCS ) R qSA
+
33 mF
qJC
is 2.5°C/watt for the CS5253B−8 in the
qCS
Remote
Connections
R
R
), and heatsink−to−ambient air
DIS
DIS
qCS
depends on factors such as
qJA
qJA
can be calculated and
qSA
+
. This total thermal
Optional
depends on the
+Load
−Load
qJC
),